HVAC Help

[bfisher]

Thanks electron and Martin. I've done some homework (I love Google) and there are many different in-line duct fans out there. I'm now learning more than I ever wanted to know about this project... Still nervous though - haven't done HVAC duct work before. And I don't want to screw up something in the main unit (although that doesn't seem likely). I'm sure you'll be seeing more from me about this one

 

[kwilcox]

Hi, I'm a new poster here and I have an extensive HVAC system that uses inline duct fans. I'm using SunCourt at present but will soon be upgrading to the quieter and more powerful vortex fans sold here.

My automation system is an X10/UPB hybrid controled by HCA. I have two zones in my ranch style house and the duct fans sit on 2 8 inch feeds between a split plenum which was moved to the center I-Beam to facilitate a soffit-free basement plan that consists of two offices and a library.

My Furnace is controlled by a UPB UMI32 I/O module made by SAI. One of the inputs is controlled by a relay attached to my blower output and is used to convey the on-off status of the system. The outputs are currently used to control the AC and Heat request lines but I'm thinking of re-deploying these. I have a TempLinc in the master bedroom which is used as the secondary thermostat.

Since cold air is denser than warm air, the automation system runs the inline fans at 66% during the cooling season and 50% during the heating season. On especially warm days, when the system hasn't cycled off in 4 hours, the automation system will switch to "max ac mode" and run the inline fans at 100%. This really improves performance. At night, the inline fans are not run which increases plenum pressure in the bedroom side of the main plenum.

I highly recommend the use of inline fans over damper systems as a component failure cannot cause a corresponding furnace failure as has been described above. I also recommend UPB over X10 due to the reliability improvements. You don't want noise to command the AC and heating components on at the same time!

I'm thinking about simply adding a seperate thermostat to the bedroom zone and using my 2 switched outputs to simply control power to the respective zones. This will prevent having to depend on X10 to provide thermostat signaling (and free up my K housecode as an added benefit).

Anyway, hope this post helps!

 

[electron]

Welcome to CocoonTech kwilcox, that's a great first post! Sounds like you got a nice setup, how is UPB working out for you? Do you need to use a coupler? I definitely like the idea of using inline fans as well, that's something I will have to investigate myself since I am not comfortable with using dampers.

 

[kwilcox]

I don't have a coupler currently, but I've got one on order. UPB, although resistant to noise, is affected by devices that actively smooth the input line voltage such as computer UPS devices. In fact, the APC 1400 UPS that I have for the office severely degrades UPB signals on the other side of the split phase. An X10 noise filter corrects this (I have an AF120 15A filter for this purpose). Interestingly, this problem occurs no matter where the ups is plugged in. My office has 2 circuits, one for my UPB PIM/houselinc that directly connects to the breaker and another that shares a 15A circuit with the rest of the plugs. The UPS problem was the same no matter which of the 2 circuits I used. With X10, the UPS dampening effect was more localized. I'm expecting a phase coupler will fix my issue though. I'll know for sure sometime next week.

Other than that, I must say that UPB is far and above X10 in terms of reliability. I'm using a PCS USB PIM and SAI US11-30 switches. I also have a lamp module. Build quality on these 1000 watt dimmers is excellent and the retail price compares to the Switchlinc 2380 2 ways. The UPB protocol itself is very powerful and you can generate some pretty complex automation without the need for a central controller using links. Advanced Quonset Technologies who makes HCA wrote the UPStart application btw, so their support of UPB in v6.1 of their software is superb. I use this software to bridge my wireless sensors onto UPB devices via a W800RF32.

 

[kwilcox]

@bfisher
Don't worry about the ductwork btw. Get yourself a good set of offset aviation tin sheers (left cut, right cut) and you'll be in business. Here's a link to my HVAC ductwork move project: Custom ductwork install June 2004.

As can be seen, I originally connected the HVAC system up using X10 powerflash and universal modules but the system wasn't reliable enough. In fact, it was this situation that promped my move to UPB.

 

[electron]

great pics, thanks for sharing!

 

[bfisher]

Thanks for the information. Is your bedroom (that the duct fan is supporting) on a second floor? or immediately above the basement? For me, the bedrooms that need the ductfan are upstairs (second floor) and the only access I have to the ducts is in the basement (we have no attic near the bedrooms).

I spoke to an HVAC company, and they said the ductfan won't work then - it needs to be closer to the vent outlets to work well.

By the way - glad to have another UPB user singing it's praises - I am really pleased with my stuff - and will be adding more very soon.

 

[rocco]

I spoke to an HVAC company, and they said the ductfan won't work then - it needs to be closer to the vent outlets to work well.

Unless it is because of forks in the ducting, that doesn't sound right. If you have a single round duct that starts in the basement and ends at a single vent in a bedroom, it would not matter where in the duct the fan is located. This assumes each bedroom vent originates with a duct in the basement.

But if you had a single larger duct that then forks off to the different bedrooms, it would be more difficult to control which rooms received the air, and having fans near the vent makes more sense.

 

[kwilcox]

HVAC design is all about CFM and air resistance. Inline duct fans simply pressurize the exhaust plenum in much the same way as the furnace blower does. As such, it theoretically doesn't matter where in the plenum they are located. Their presence will increase airflow at all downstream diffusers. What is less obvious is this: They will also decrease airflow at all upstream diffusers, even if the primary furnace blower sits between them and the affected diffusers. If you think about this, it makes sense too.

That being said, some fans are more efficient than others at doing this. My research has indicated that centrifigual designs like the fantech and vortex products are quieter, and more powerful than their blade oriented counterparts. More importantly, centrifigual fan efficiency doesn't drop off at the same rate as the downstream pressure increases as do blade fans. Thus the reason for your HVAC guy's statement I believe. If you place a blade fan near a diffuser, the downstream back pressure is essentially zero, thus maximizing the efficiency. My Suncourt fans are designed for high pressure downstream applicatons so they work well in my HVAC setup. My chief complaint with them is that they tend to "ring" at certain RPM's. This is why I want to upgrade to Vortex (or, I may just experiment with different blade designs to eliminate this)

Hope this helps!

 

[kwilcox]

As far as UPB goes, I'm finding that the X10 universe of daily changes in reliability have disappeared. I was getting really frustrated with my system which seemed to have "good" and "bad" days with no changes or additions, for no apparent ryme or reason. Sound familiar? UPB is stable. It works the same way all the time. The protocol also has built in testing and diagnostic capabilites. This is huge to me as I can bring up a built in monitor in UPStart to display signal strength and noise level at my PIM and at the device itself. As an installer, I empathize with my clients who want their automation systems to have the reliability of a light switch. X10 never was good enough in this respect. UPB is. Plain and simple. I'm sold on it.

 

[bfisher]

Thanks for the excellent information kwilcox! I will research this some more... the ducts in my basement all appear to be rectangular (and fairly big), and their fans all appear to be round - not sure if these can be made to work together or not. I assume they are rectangular until they get up to the second floor and then they become round as they go to the vent outlets.

I will give them a call tomorrow and find out pricing and if they have local installers they can recommend. If not, I might try your suggestion and do it myself, but that is one area I have no expertise. Especially with the rectangular to round issue...

 

[electron]

in my house, rectangular ducting is used for the main run, and round ones are used to branch off to each room.

 

[kwilcox]

@bfisher:

Hmmm... your system might also use square ductwork designed to fit between studs for the upstairs runs. That would complicate a boost fan oriented system. However it would also complicate a damper based implementation as well. One thing you could do would be to remove a section from your primary air flow plenum and insert a vortex fan coupled to two square end-caps there. That way the fan would sit in the plenum itself and the restriction would decrease airflow in the downstream zone and increase airflow in the other if the fan wasn't operational. Of course. this assumes that your bedroom zone can be isolated to one section of the primary plenum. However, in many multiple floor houses built since the advent of the "master bedroom suite" concept, this simply isn't the case. That's one thing I've always liked about the ranch-style single floor layout. There's generally one outflow plenum having the furnace in the middle with one side feeding the bedroom zone and the other feeding the living area. It simplifies a duct fan based implementation for sure!

 

[bfisher]

thanks for the additional info.

My dampers are large and rectangular as well and are located in the basement (within 6 feet of the HVAC central unit).

Can you define plenum for me? I've been assuming it's the ductwork itself, but now I'm not sure...

I would be happy if the entire upstairs zone got increased airflow - not just the master bedroom (in fact, the MBR seems to have the best airflow already). Not sure if adding a ductfan in the main ducting going to the upstairs zone would be able to increase airflow enough to feel the improvement after it's been divided into 4 vents...

 

[kwilcox]

Sure. Plenum is the primary ductwork that directly attaches to your furnace. Usually there's two: one for output and one for air return. Your room diffusers usually connect via ductwork that attaches to the output Plenum via a "takeoff" fitting on the plenum itself. Plenum usually runs perpendicular to and consequently underneath your floor joists, so most takeoffs are "top takeoffs" attached to the top of the plenum which connect to runs that are parallel to and between floor joists. If you follow the link to my little project, you can see that I actually moved half of my output plenum to the middle of the basement, connecting the two with a pair of 8" runs between top takeoffs. Its on these two 8 inch runs that the boost fans sit. There's also several pics of the 6" runs that connect to my diffusers.